The present invention relates to the art of diagnostic imaging. It finds particular application in conjunction with single-photon emission computed tomography (SPECT) with multi-headed cameras and will be described with particular reference thereto. It is to be appreciated, however, that the invention will also find application in other non-invasive investigation techniques such as positron emission tomography (PET) and other diagnostic modes in which a subject is examined for emitted radiation.
Heretofore, single photon emission computed tomography has been used to study the radionuclide distribution in subjects. Typically, one or more radiopharmaceuticals were injected into a patient. The radiopharmaceuticals were commonly injected into the patient's blood stream for imaging the circulatory system or for imaging specific organs which absorb the injected radiopharmaceuticals. Gamma or scintillation camera heads were placed closely adjacent to a surface of the patient to monitor and record emitted radiation. In single photon-emission computed tomography, the head was rotated or indexed around the subject to monitor the emitted radiation from a plurality of directions. The monitored radiation data from the multiplicity of directions was reconstructed into a three dimensional image representation of the radiopharmaceutical distribution within the patient.
SPECT systems typically use one or more large field of view gamma camera heads that rotate about the patient. When cone-beam collimation was used with these systems, the source distribution was not sampled sufficiently. Blurring artifacts occurred with filtered backprojection reconstruction, particularly for sources located away from the central slice.
Maximum likelihood approaches using an expectation-maximization algorithm have resulted in improved image quality for cone-beam SPECT systems as compared with filtered backprojection methods. However, because the cone-beam projection data acquired using a single circular orbit were inherently incomplete in the axial direction, image distortions could not be entirely eliminated. Furthermore, truncation artifacts resulted for sources that were outside the field of view of the cone-beam collimator at certain times during the scan. Other systems have attempted to reduce axial truncation artifacts by combining simultaneously acquired parallel beam and cone-beam data.
The present invention contemplates a new and improved simultaneous transmission and emission tomography method and apparatus which overcomes the above-referenced problems and others.